Rhigh boiling



March 10, 1964 R. M. BUTLER ETAL 3,124,526

HYDROFINING PROCESS FiledJuly 11, 1960 I5 SEPARATOR l7 '4 Z HYD OGEN- I6conmmms GAS 22 I8 7 2o 19 REFLUX NAPHTHA PRODUCT HEAT-SENSWWE/REACTOR-FRACT|ONATOR NAPHTHA-FEED HYDROGEN 24 HIGH 'soluus HIGH BOILINGFEED o|| PRODUCT Roger M. Butler Jackson Eng Inventors BY 1 M,

fi Patent Attorney United States Patent Ofiice 3,124,526 Patented Mar.10, 1964 3,124,526 HYDROFINlNG PROCESS Roger M. Butler and Jackson Eng,Sarnia, Ontario, Canada, assignors to Esso Research and EngineeringCompany, a corporation of Delaware Filed July 11, 1960, Ser. No. 41,9744 Claims. (Cl. 208264) This invention relates to a hydrocarbonconversion process and more particularly to an improved process for thecatalytic conversion of heat sensitive naphthas in the presence of addedhydrogen.

It is known that the quality of virgin or straight run as well ascracked or thermally reformed naphthas and middle distillates can beimproved by reacting such feedstocks with added hydrogen at elevatedtemperatures and superatmospheric pressures in the presence ofhydrogenation-dehydrogenation catalysts. Such operations are referred toas hydroforming, hydrofining, hydrocracking, hydrodesulfurizing, and thelike. The purpose and result of these treatments are to effect asubstantial reduction in the sulfur content, to saturate certain highlyunsaturated gum-forming constituents and to saturate at least a part ofthe olefins present, to improve the color and odor of the product and toproduce aromatic hydrocarbons by the catalytic dehydrogenation ofnaphthenic and cyclic olefin components.

In most of these processes the feed is supplied alone or in admixturewith the added hydrogen-rich treat gas to the catalyst-containingreaction zone at temperatures in the range of from about 450 F. to 950F. It is the general practice to obtain such temperatures by passing thefeed through a heat exchanger or furnace provided with a large number oftubes of small diameter. It has been found, however, that astemperatures above about 250350 F. are reached, many naphtha feeds tendto form deposits upon the walls of the heat exchanger which in somecases have completely plugged the heat exchanger tubes. In addition,these feeds have a tendency to form excessive amounts of carbonaceousdeposits upon the catalyst severely reducing the activity thereof.

It has been proposed to overcome these difficulties in various ways suchas by passing an inert gas through the feed stock to strip off the freeoxygen content, by blanketing the feed stock with an inert gas tominimize contact with air and by giving the feed stock a pretreatmentwith hydrogen in contact With a hydrogenation-dehydrogenation catalystat temperatures above about 300 F. but below the temperature at whichsubstantial deposits are formed.

It is the object of this invention to provide an improved process forhydrofining heat-sensitive naphthas.

It is a further object of this invention to provide a process forhydrofining heat-sensitive naphthas which avoids the problems of depositformation on heat exchanger surfaces and overcomes the problem ofexcessive carbonaceous deposit formation upon the catalyst.

These and other objects will appear more clearly from the detailedspecification and claims which follow.

It has now been found that heat-sensitive naphthas such as cracked orcoker naphtha can be effectively hydrofined without the usual heatexchanger and catalyst fouling by mixing the naphtha feed with asuitable gas oil, pumping the feed mixture in the liquid phase into thecenter section of a high pressure reactor-fractionator tower which issuitably packed with hydrofining catalyst. The hydrogen or hydrogen-richtreat gas stream is injected into the reboiler at the bottom of thetower whereupon the treat gas passes upwardly through the tower,countercurrently to the descending gas oil in the lower portion of thetower and concurrently with the naphtha in the upper section of thetower. The operation of the reactor-fractionator tower is very much likeany fractionator. The pressure, hydrogen rate and the boil-up rate arechosen so as to give the desired separation as well as the desireddegree of hydrofining. The hydrofined naphtha product is taken overheadfrom the tower while the gas oil is removed as bottoms. The principaladvantages of the process in accordance with the present invention isthat vaporization of the heat-sensitive naphtha feeds in heat exchangeror preheat furnace tubes is avoided and moreover the entire catalyst bedis being continuously washed with a hot liquid oil phase.

The feed stocks that can be treated advantageously by the process of thepresent invention are those hydrocarbons which boil within the range offrom about to 450 F. and may be straight run naphtha, coker naphtha,thermally cracked naphtha and catalytically cracked naphtha. The processof this invention is particularly adapted for the treatment of crackedor coker naphthas, especially those which tend to form deposits whenheated to temperature of about 250350 F. in heat exchangers or preheatfurnace tubes.

The higher boiling oil which is added to the naphtha feed stock inaccordance with the present invention should boil within the range offrom about 450 to 800 F. preferably 550 to 650 F. The higher boiling oilmay be a virgin gas oil which will be desulfurized in the operation orthe higher boiling oil may, if desired, be recycled in whole or in part.

For operability of the invention the ratio of heavy oil to naphtha inthe feed is not very critical. The reason for this is that by refluxingvapor up the column from the reboiler the heavy oil concentration may bemaintained even though it is not being added in large quantities in thefeed. However, in order to prevent the accumulation of extracted polymerin the reboiler some constant addi tion and withdrawal of heavy oil isnecessary. The minimum quantity of this heavy oil addition will dependupon the materials being processed, the particular catalyst being usedand upon the severity. In general, it is expected that most operationswill require a minimum of about 0.1 volume of heavy oil per volume ofnaphtha.

There is no maximum to the amount of heavy oil which can be added andthe quantity used will be controlled by its availability together witheconomic com parisons with other methods of treatment.

Any conventional hydrofining or hydrogenationdehydrogenation typecatalyst may be used. Such catalysts include various oxides and sulfidesof metals of groups VI and VIII such as molybdenum, tungsten, chromiumor the like or mixtures such as nickel-tungsten sulfide and cobaltmolybdate or mixtures of cobalt oxide and molybdenum oxide preferablydeposited upon a support or carrier material such as activated alumina,silica gel, or activated alumina containing small amounts (2 to 10 wt.percent) of silica. The preferred catalyst is one containing from about5 to 25 wt. percent of cobalt oxide and molybdenum oxide with the ratioof the former to the latter in the range of from about one to five toabout five to one, supported upon an adsorptive or activated aluminacontaining about 0 to 5 wt. percent of silica. Such catalysts areprepared by first forming adsorptive alumina, containing silica ifdesired, in any suitable or known way and then compositing molybdenumoxide and cobalt oxide therewith. The molybdenum oxide can, for example,be added as a slurry or it may be applied as a solution of ammoniummolybdate. The cobalt oxide is conveniently added as a salt such ascobalt nitrate or acetate, salts which are readily decomposed to cobaltoxide and volatile materials. The catalysts may, if desired,,be given anactivation treatment prior to use in the hydrofiner by reacting the samewith a suitable sulfiding agent such as a sulfur-containing feed stock,

hydrogen sulfide, carbon disulfide and the like. The amount of sulfuradded for preactivation of the catalyst may vary from about 100% up toabout 1500% of the stoichiometric quantity necessary to convert thecobalt oxide and molybdenum oxide to the corresponding sulfides.

The reaction conditions maintained in the reactor fractionator vesselvary somewhat depending upon the nature of the feed stock, the characterand quantity of the impurity or contaminant being removed and the degreeof improvement desired. In general, the reaction temperature is about400 to 800 F. preferably 500 to 650 F., reaction pressure 50-500p.s.i.g., preferably 200-250 p.s.i.g. and feed rate is 0.5 to 20v./v./hr.; preferably about 1-3 v./v./hr. The hydrogen-rich treat gas,which should contain at least about 30 volume percent hydrogen issupplied to the bottom of the reactor-fractionator column at the rate ofabout 50 to 2000 s.c.f./b., preferably about 1000 s.c.f./b. and thehydrogen consumption in the hydrofining operation is about 100 to 500s.c.f./b., usually about 300 s.c.f./b.

Reference is made to the accompanying drawing illustratingdiagrammatically the reactor-fractionator used in the present invention.

In the drawing, liquid feed stock comprising a mixture of a naphthafraction and a gas oil or higher boiling fraction is supplied at systempressure through inlet line 10 at temperatures of about 200 to 600 F.The liquid feed mixture is supplied at or about the midpoint of thereactor-fractionator 11 which is charged with a suitable hydrofining orhydrogenation-dehydrogenation type catalyst.

The catalyst bed and/r inert packing provided in the vessel 11 serve topack the vessel so that it can serve as a fractionator. For example,diameter, /8" long hydrofiner catalyst particles as a packing is about 1to 2 feet HETP (height equivalent to a theoretical plate). A heatingcoil 12 is arranged at the bottom of the vessel to supply the necessaryheat for vaporizing the higher boiling oil fraction. Hydrogen-rich treatgas is supplied through inlet line 13 at the bottom of the vessel 11 andserves to assist in the vaporization of the higher boiling oil fraction.The hydrogen-containing gas passes up Wardly through the column countercurrently to the downfiowing heavy oil and reflux in the lower portionof the column and concurrently with the lighter naphtha vapors in theupper part of the column. Temperatures at the bottom of the column areabout 600750 F. while temperatures at the top are in the range of fromabout 400-600 F. Pressures within the column are about 50-500 p.s.i.g.,preferably 200-250 p.s.i.g. and under these conditions the hydrogenationof sulfur, nitrogen, and, to some extent, the olefinic compounds in theoils are promoted.

The hydrofined naphtha, excess treat gas and gaseous reaction productspass overhead from vessel 11 through line 14, cooled in condenser 15 anddischarged into separator 16. Gaseous products are released from the topof separator 16 via line 17 and after absorption may be used as fuel or,if desired, scrubbed of hydrogen sulfide and the like and recycled tothe reactor-fractionator. Naphtha product is withdrawn from separator 16through line 18 and 19 and discharged to a stripper and/or furtherprocessing such as hydroforming. A portion of the naphtha product isrecycled via line 20, pump 21 and line 22 as reflux to the top of thereactor-fractionator. It should be noted that in the arrangement shown,all of the catalyst within the vessel is continuously washed by the flowof liquid oil thereover. This is especially advantageous since the heatsensitive naphthas such as coker or catalytically cracked naphthasnormally tend to form large amounts of carbonaceous deposits upon thecatalyst which in the present invention are continuously removed by thewashing action of the oil. Moreover, by mixing the heat sensitivenaphtha which tends to form deposits on heat transfer surfaces whenvaporized, with gas oil and supplying the feed stream to the reactorfractionator vessel in liquid form, the vaporization of the naphtha iseffected in an area where the surfaces of the catalyst, filler orpacking materials as well as the walls of the vessel itself arecontinuously washed with liquid oil. This should give high heat economywith small capital investment.

The higher boiling oil is withdrawn from the bottom of the columnthrough line 23 and discharged to product storage via line 24 or, ifdesired, a portion of the heavy oil may be pumped via line 25 back tothe feed inlet line 10 as recycle.

The following example is illustrative of the present invention.

Example A heat sensitive C /430 steam cracked naphtha is to behydrofined to improve stability by the partial saturation of diolefins.It is mixed in approximately equal volumes with a 430/650 virgin gasoil. This virgin gas oil is to be desulfurized for use as diesel fuel.The mixed feed is fed at a temperature of about 300 F. into the centerof the combination reactor-fractionator. This vessel is packed with amixture of cobalt molybdate on alumina catalyst and a suitabledistillation packing such as Berl saddles. The catalyst may be in theform of pellets, cylinders, spheres or in various extruded shapes suchas hollow cylinders, saddles, etc. The height and diameter of the towermay be chosen by methods well known to those skilled in the art. Thediameter must be suflicient so that with the vapor and liquid loadingsrequired, flooding will not occur. The height must be sufi'icient toprovide adequate fractionation. These requirements fix the total volumeof catalyst and inert packing. The volume of active catalyst required ineach section, i.e. above and below the feed injection point, will bedetermined by the required qualities for the naphtha and gas oilproducts. In general, the total volume of catalyst will be in the rangeof 0.1 to 1.0 multiplied by the total hourly liquid volume of feed.

For the particular example described here, the reactor operatingpressure is 200 p.s.i.g., the hydrogen gas treat rate is 1000 s.c.f./b.,the temperature is 650 F. in the reboiler, and at the top of the tower490 F. An external reflux ratio of 1:1 is employed. The inspections onthe feed components are given below:

Bromine No Diene No Research Octane No.

The naphtha is to be treated to a diene number of less than 2. The gasoil sulfur content is to be reduced to less than 0.4.

For these requirements, it is found that an equal volume of catalystshould be used both above and below the feed plate and that the totalvolume of catalyst should be in the range of 0.5 to 1.0 times the totalhourly liquid feed rate. A total column height of 30 to 40 feet wouldgive fractionation satisfactory for most purposes.

The foregoing description contains a limited number of embodiments ofthe present invention. It will be understood that numerous variationsthereof are still within the scope of the present invention.

What is claimed is:

1. The method of catalytically hydrogenating heat sensitive naphtha feedstocks that tend to form a deposit upon a heat transfer surface whenpreheated to a temperature above about 250-350 F. and which tend to forman excessive amount of carbonaceous deposit upon hydrogenating catalystin a reaction zone, which comprises mixing the said naphtha feed stockwith a higher boiling gas oil, introducing the resultant mixture atabout the mid-section of a vertical reaction zone containing ahydrogenation-dehydrogenation catalyst, supplying heat to said reactionzone and maintaining it at a temperature of about 400-800 F. and at apressure of about 50-500 p.s.i.g. to vaporize said naphtha in saidreaction zone and at least a portion of the gas oil, passing naphthavapors upwardly through the upper portion of said reaction zone,supplying hydrogen-containing treat gas to the bottom of said reactionzone and passing said gas upwardly through said reaction zonecountercurrently to the descending gas oil in the lower portion of thezone and concurrently with the naphtha vapors in the upper portion ofsaid reaction zone, removing hydrofined naphtha product overhead fromthe said reaction zone, removing liquid gas oil as bottoms from saidreaction zone, condensing hydrofined naphtha product and returning aportion of said liquid hydrofined naphtha product to the top of saidreaction zone to maintain liquid oil in contact with catalyst in theupper portion of said reaction zone.

2. The method of catalytically hydrogenating heat sensitive naphtha feedstocks that tend to form a deposit upon a heat transfer surface whenheated to temperatures above about 250350 F. and which tend to form anexcessive amount of a carbonaceous deposit upon the hydrogenatingcatalysts which comprises mixing the said naphtha feed stock with ahigher boiling gas oil, introducing the resultant mixture at about themid-section of a vertical reaction zone containing ahydrogenationdehydrogenation catalyst, maintaining said reaction zone ata temperature of about 400-800 F. and a pressure of about 50-500p.s.i.g. by supplying heat to the bottom of said zone to vaporize thenaphtha in said reaction zone and at least a portion of the gas oil insaid reaction zone, supplying hydrogen-containing treat gas to thebottom of said reaction zone and passing said treat gas upwardly throughthe reaction zone countercurrently to the descending gas oil in thelower portion of said reaction zone and concurrently with the naphthavapors in the upper portion of said reaction zone, removing hydrofinednaphtha product overhead from the said reaction zone, condensing thehydrofined naphtha product, recycling a portion of the liquid naphthaproduct to the top of said reaction zone to maintain liquid oil incontact with the catalyst in the upper portion of said reaction zone andremoving hydrofined liquid gas oil as bottoms from said reaction zone.

3. The method of catalytically hydrogenating heat sensitive naphtha feedstocks that tend to form a fouling deposit upon a heat transfer surfacewhen preheated to a temperature above about 250-350" F. and which tendto form an excessive amount of a carbonaceous deposit upon ahydrogenating catalyst in a reaction zone, which comprises mixing thesaid naphtha feed stock with a higher boiling gas oil, introducing theresultant mixture below said fouling temperature of 250-350 at about themid-section of a vertical reaction zone containinghydrogenation-dehydrogenation catalyst and maintained at a temperatureof about 400-800 F. and a pressure of about 50-500 p.s.i.g., supplyingheat to the bottom of said reaction zone in suificient amount tovaporize the naphtha and at least a portion of the gas oil, supplyinghydrogen-containing treat gas to the bottom of said reaction zone,recycling a portion of the condensed hydrofined naphtha product referredto hereinafter, to the upper portion of said reaction zone to maintainliquid oil in contact with the catalyst within the upper portion of saidreaction zone, removing hydrofined naphtha product overhead from thesaid reaction zone, condensing the hydrofined naphtha product, removinghydrofined liquid gas oil as bottoms from said reaction zone, andrecycling a portion of said hydrofined liquid gas oil to the inlet ofsaid reaction zone for mixing with fresh feed naphtha.

4. The method of catalytically hydrogenating heat sensitive naphtha feedstocks that tend to form a deposit upon a heat transfer surface whenheated to a temperature above about 250-350" F. and which tend to forman excessive amount of carbonaceous deposit upon a hydrogenatingcatalyst in a reaction zone which comprises mixing the said naphtha feedstock with a higher boiling gas oil, introducing the resultant mixtureat a temperature of about 250-350 F. about the mid-section of a verticalreaction zone containing a hydrogenation-dehydrogenation catalyst andmaintained at a temperature of about 490-650 F. and a pressure of about50-500 p.s.i.g., supplying heat to the bottom of said zone in suflicientamount to vaporize the naphtha and at least a portion of the gas oil,supplying hydrogen-containing treat gas to the bottom of said reactionzone and passing the treat gas upwardly through said reaction zonecountercurrent- 1y to the descending gas oil in the lower portion ofsaid reaction zone and concurrently with the naphtha vapors in the upperportion of said reaction zone, removing hydrofined naphtha productoverhead from the said reaction zone, condensing the hydrofined napthaproduct, recycling a portion of the liquid naphtha product as reflux tothe top of said reaction zone to maintain liquid oil in contact with thecatalyst in said reaction zone, removing hydrofined liquid gas oil asbottoms from said zone, and recycling a portion of said hydrofinedliquid gas oil for admixture with fresh feed naphtha to be introducedinto said reaction zone.

References Cited in the file of this patent UNITED STATES PATENTS2,608,521 Hoog Aug. 26, 1952 2,844,517 Inwood July 22, 1953 2,897,143Lester et a1 July 28, 1959 2,952,626 Kelly et a1 Sept. 13, 19602,958,654 Honeycutt Nov. 1, 1960

1. THE METHOD OF CATALYTICALLY HYDROGENATING HEAT SENSITITIVE NAPHTHAFEED STOCKS THAT TEND TO FORM A DEPOSIT UPON A HEAT TRANSFER SURFACEWHEN PREHEATED TO A TEMPERATURE ABOVE ABOUT 250-350*F. AND WHICH TEND TOFORM AND EXCESSIVE AMOUNT OF CARBONACEOUS DEPOSITE UPON HYDROGENATINGCATALYST IN A REACTION ZONE, WHICH COMPRISES MIXING THE SAID NAPHTHAFEED STOCK WITH A HIGHER BOILING GAS OIL, INTRODUCING THE RESULTANTMIXTURE AT ABOUT THE MID-SECTION OF A VERTICAL REACTION ZONE CONTAININGA HYDROGENATION-DEHYDROGENATION CATALYST, SUPPLYING HEAT TO SAIDREACTION ZONE AND MAINTAINING IT AT A TEMPERATURE OF ABOUT 400*800*F.AND AT A PRESSURE OF ABOUT 50-500 P.S.I.G. TO VAPORIZE SAID NAPHTHA INSAID REACTION ZONE AND AT LEAST A PORTION OF THE GAS OIL, PASSINGNAPHTHA VAPORS UPWARDLY THROUGH THE UPPER PORTION OF SAID REACTION ZONE,